The typical battery charger used by a homeowner is one which operates from 60 hertz, 120 volt power source and has a step down transformer wherein the voltage is rectified and applied to the battery. Such typical battery charger has a tapering current rate which decreases as the terminal voltage of the battery increases as it is charged. Also such battery charger typically has voltage at the battery charger output terminals or battery output clips as soon as the charger is energized by plugging the typical cord and plug set into a convenience outlet. As a result, there is a danger of sparks at the connection to the battery should the battery charger be energized prior to connection of the charger to the battery. Such sparks are dangerous due to the generation of hydrogen in the charging of a typical lead-acid battery.
Should such conventional battery charger remain connected to the battery it will continue to trickle charge the battery which can cause severe outgassing and generally is not recommended for lead acid batteries.
A prior U.S. Pat. No. 3,688,177 had proposed a circuit for variable charging rates depending on the charged state of the battery and provides a high charging rate to a first predetermined voltage per cell, then a medium charge rate to a lower predetermined voltage per cell and then zero amperes even though the charger remains connected to the battery. The charging may restart when the voltage becomes less than a third predetermined voltage per cell.
U.S. Pat. No. 4,243,929 discloses a circuit wherein a battery is charged at a high rate until charged and then the charging current is reduced to a low level. When the battery voltage drops below a predetermined limit, the trickle charging current is again increased to the higher level.
The prior art battery chargers generally fail to provide a means to safely and efficiently charge a battery in a short length of time, or they continue to charge the battery after it is fully charged therefore creating outgassing. The problem to be solved therefore is how to construct a battery charger which will eliminate the foregoing problems yet will be capable of recharging the battery should the battery voltage fall below a predetermined voltage value.